The invention relates to a push-button actuated overload protection switch and, in particular, to an on-board electrical system protection switch with manual actuation and bimetal controlled automatic tripping.
Known overload protection switches comprise a housing, a switch latch trippable by a push-button for bringing a contact bridge into a contact closing position and a contact opening position relative to mating contacts fixed to the housing; and a bimetallic tripping device for releasing the switch latch, including a self-heating bimetal in the form of an approximately U-shaped punched member which is electrically connected in series to the path of current through the switch. The free end of one arm of the U-shaped punched member is fastened to one end of a connecting lug fastened within the housing of the switch. The free end of the second arm is fastened to a connecting piece to which one of the mating contacts is attached. The base of the U-shaped punch member of the bimetal is deflectable in response to current flowing therethrough and is kinematically connected with the switch latch.
Such overload protection switches are disclosed, for example, in DE-C 2,123,765 and EP-A 0,081,290. In these switches, the bimetal of the bimetal tripping device is disposed essentially parallel to the narrow side wall of the switch housing, when viewed from the direction of pressure (D) applied to the push-button. Adjustment is effected by means of an adjustment screw which passes through a bore in this side wall and acts laterally and directly onto the bimetal and on its connecting foot.
The accuracy of the bimetal adjustment in the prior art switches leaves something to be desired. Moreover, direct charging of the bimetal and its connecting foot should be avoided.
In the overload protection switch disclosed in U.S. Pat. No. 3,697,915, there is already an improvement in this respect. In this device the connecting lug and the region adjacent the mating contact fixed to the housing on a connecting piece are tightly held in an accurate fit in corresponding bearing recesses in the housing. Moreover, the bimetal is not directly charged, but the connecting piece in the region within the housing is charged by an adjustment screw inserted laterally into the switch housing. In order to facilitate the adjustment displacement of the part of the connecting piece that is disposed in the interior of the housing, a reduction in cross section in the form of recesses in the lateral faces of the connecting piece is provided between the region where the connecting piece is fixed to the housing and the region where it is charged by the adjustment screw.
Furthermore, DE-U-88 06 964.8 discloses an electrical overload switch in which the strip-shaped bimetal is fastened to a connecting piece that is likewise held tightly and in a precise fit in corresponding supporting gaps in the housing. This connecting piece has an extension which is charged by an adjustment screw from the opposite side of the switch housing to adjust the response value of the bimetal.